Changes in free amino acids of tempe during preparation with velvet beans (Mucuna pruriens)

Abstract

Tempe was prepared with velvet bean using pure cultures of Rhizopus oligosporus (IFO 8631) and consequent changes in free amino acids content were examined. A ninhydrin positive unknown compound detected as methionine in an amino acid analyzer chromatogram was isolated by ion-exchange and gel-filtration column chromatographies and identified. The compound was determined as 3,4-dihydroxyphenylalanine (DOPA). Total content of free amino acids of tempe was 0.8 g/kg dry beans, corresponded to 17% of that of dry beans. Most free amino acids unchanged in the 1st soaking and boiling, decreased in the 2nd and 3rd soakings, and increased during fermentation. Their content decreased by 7% on dehulling. DOPA which was abundant in velvet bean decreased in the 2nd and 3rd soakings, and 30% DOPA of that of dry beans remained in tempe.